In spite of antibiotics, pneumococcal disease is still the leading cause of death by infectious agents in the United States. In children it is the leading cause of otitis media and as such accounts for most of the sick baby visits for pediatric care. Meningitis caused by pneumococci is frequently fatal in infants. The increased incidence of antibiotic-resistant pneumococci suggests that this situation may get even worse. The present pneumococcal vaccine consists of a mixture of the capsular polysacharides from the pneumococcal types most commonly associated with infection. Although this vaccine affords good immunity in adults, it is not effective in young children because they do not develop the ability to respond to polysaccharides until they reach the age of 6 months to 2 years. In this grant we describe studies to determine the role of pneumococcal surface proteins in pathogenicity and to examine whether these proteins can be used to elicit protective immunity against pneumococcal infection. We have recently demonstrated that hybridoma antibody to a pepsin-sensitive antigen present on a type 3 pneumococcal strain can protect mice from fatal pneumococcal infection. We plan to produce additional hybridoma antibodies to the surface proteins of pneumococcal strains with capsular types commonly associated with childhood infections. We will use these antibodies to aid in cloning the genes that code for these proteins into E. coli. The cloned pneumococcal genes will then be placed in high expression vectors for the production of large amounts of these proteins, which will be isolated with the aid of the hybridoma antibodies, and tested in mice to see if they might serve as potential vaccine components. We will also use the hybridoma antibodies to isolate and characterize mutant pneumococci to further evaluate the importance of these protein antigens in pneumococcal virulence.